To increase the integration of semiconductor devices efforts must be made to improve the yield, performance and reliability of the highly integrated semiconductor devices. As metal interconnection technology is one of the most important steps in the semiconductor device manufacturing process, improvements in the metal interconnection technology can result in improvements in the yield, performance and the reliability of integrated devices. In a conventional low density semiconductor device, burial of a contact hole by a metal did not present difficulties because, in general, the contact hole in a low density semiconductor device has a low aspect ratio and small step difference.
As integration of devices has increased, the size of the contact hole has been reduced remarkably. If a conventional aluminum (Al) metal interconnection method is adopted for manufacturing a highly integrated semiconductor device, step coverage of the aluminum deposited by sputtering becomes poor due to the high aspect ratio of the contact hole. Thus, the reliability of the aluminum interconnection is lowered. Also, shallow junction characteristics are deteriorated because of the increase in contact resistance caused by the precipitation of silicon and aluminum spiking.
FIGS. 1 to 3 are sectional views illustrating a conventional method of manufacturing a semiconductor device in which a contact hole is buried with a metal. FIG. 1 shows the step of forming a first metal layer. As seen in FIG. 1, a contact hole 5 of diameter 0.8 .mu.m has and upper portion in the shape of a staircase. The contact hole 5 is formed on an insulating layer 3 of a semiconductor device. After the insulating layer 3 is formed, the semiconductor substrate 1 is cleaned. Subsequently, a barrier layer 7 made of refractory metal compound such as TiN is deposited on the insulating layer 3 and the exposed surface of the substrate 1. Then, a metal such as pure aluminum or aluminum alloy is deposited on the barrier layer 7 in a sputter chamber (not shown), to form a first metal layer 9. The first metal layer 9 has small grains and high surface free energy and is deposited at a low temperature and predetermined vacuum to a thickness of two-thirds the thickness of the final thickness of the metal layer 9.
FIG. 2 shows the step of burying the contact hole 5. As illustrated in FIG. 2, when the first metal layer 9 is heated at about 580.degree. C. in a sputter chamber (not shown) without vacuum break, the aluminum grains are moved to the contact hole 5. The movement of the aluminum grains decreases the surface energy, so that the surface area decreases and the contact hole 5 is buried with aluminum, as shown in FIG. 2.
FIG. 3 illustrates the step of forming a second metal layer 11 on the first metal layer 9. The second metal layer 11 is deposited on the first metal layer 9 at 350.degree. C. or below, to a thickness of one-third the desired final thickness of the metal layer. The second metal layer 11 is made of aluminum alloy including silicon, such as Al-Si or Al-Cu-Si. Subsequently, the second metal layer 11, the first metal layer 9 and the barrier layer 7 are patterned to complete the formation of the metal interconnection.
As illustrated in FIGS. 4 and 5, in the semiconductor device formed according to the conventional method, the contact hole may be incompletely buried. FIGS. 4 and 5 are photographs taken by a scanning electron microscope (SEM), showing the cross-section of the contact hole of the semiconductor device which is incompletely buried, according to the conventional method.
In the conventional method, the step of burying the contact hole 5 shown in FIG. 2 occurs while the first metal layer 9 is heated. During heating, the contact hole 5 is buried with aluminum by the movement of metal atoms. However, the contact hole 5 may be incompletely buried by the conventional heating process of heating at a temperature of 580.degree. C. for 90 seconds, as FIGS. 4 and 5 illustrate.
The degree to which the contact hole 5 is buried by the metal depends on the shape, size and aspect ratio of the contact hole, and the heating time and temperature. As shown in FIGS. 4 and 5, the contact hole may be incompletely buried when the aspect ratio of the contact hole is high. The most effective factor in increasing the degree to which the contact hole is buried is the heating temperature. That is, when the heating temperature is high, the contact hole can be completely buried. However, the high temperature causes a spiking of the metal layer which deteriorates the electrical characteristics in the metal connection. Therefore, it is undesirable to increase the heating temperature to a temperature sufficient to completely bury the contact hole with metal.